1. Field of the Invention
The present invention relates to a hydraulic valve driving device that drives an engine valve using hydraulic pressure and an engine including the hydraulic valve driving device and a vehicle including the engine.
2. Description of the Background Art
There have been conventionally known hydraulic valve driving devices that drive an engine valve including an intake valve and an exhaust valve using oil pressure (see, for example, JP 5-202710 A).
Such a hydraulic valve driving device is provided with a hydraulic pump operable to generate oil pressure. In the hydraulic valve driving device disclosed by JP 5-202710 A, at the time of engine starting, the intake valve and the exhaust valve are prevented from operating before the oil pressure in the hydraulic pump reaches a prescribed value or higher, so that the intake valve and the exhaust valve are allowed to operate in a stable manner.
In the hydraulic valve driving device disclosed by JP 5-202710 A, the hydraulic pump is generally driven by a crank in the engine.
In the hydraulic valve driving device that drives the hydraulic pump by the crank, however, the hydraulic pump is driven together with the engine itself whose inertia is large, and therefore the rotation speed of the hydraulic pump is not quickly raised. Therefore, it takes long for the oil pressure to be raised, and therefore it takes long before the engine valve is driven stably. This makes it difficult to conduct quick and good engine starting.
At the time of engine starting, the crank must be driven with high torque in order to overcome the initial compression stroke. The viscosity of operation oil for the hydraulic pump is high. As described above, it is necessary to drive the crank requiring high torque and the hydraulic pump with the operation oil having high viscosity at the same time for the purpose of increasing the oil pressure, which requires a large amount of energy. Consequently, necessary oil pressure cannot be obtained instantaneously and good engine starting cannot be carried out.